Intervertebral disc degeneration is a common malady which produces low back pain, resulting in disability and in the U.S. health care cost exceeding $100 billion per year. The intervertebral discs are partially movable joints that connect vertebral bodies in the spine. These discs function both to transfer the weight loads and impart mobility. Surgical treatment for symptomatic disc diseases consist of removal of degenerated disc and fusion of the adjacent vertebral bodies, as well as by application of screws, plates and cages. These modalities alter the normal physiology of the vertebral segment. To avoid complications and disadvantages of a spine segment immobilization, regeneration of the intervertebral disc would be preferable. Much effort had been exerted in this direction. Attempts to effect intervertebral disc regeneration included alteration of the phenotype of cells active in the disc, by introducing new cell population, and growth factors, particularly BMP7 and sonic hedgehog (Shh).
Low back pain affects a large number of people. In the U.S. the economic impact exceeds $100 per year. In the majority of patients low back pain is caused by the degenerative changes in the intervertebral disc. The etiology of disc degeneration had not been established with certainty, but its progression is related to aging. Disc degeneration can be viewed as a cascade of events that begins with changes of extracellular microenvironment within the substructure of the disc that progresses with time to anatomic alterations resulting in pathological changes and functional impairment.
As opposed to typical joints of the limbs where mobility is the most important factor and stability is achieved by the supportive soft tissues, the joints of the vertebral column are characterized by stability and resistance to mechanical stress with limited mobility. The connection between the vertebral bodies is unique, as it allows significant degree of movement while withstanding high loads as well as deforming forces.
The intervertebral disc consist of three parts, each made up of different types of connective tissue. The central gelatinous nucleus pulposus is contained by annulus fibrosus which connects the vertebral bodies. Annulus fibrosus is attached to the cartilaginous vertebral end-plate which also contains on osseous component.
The cartilaginous end-plates are integral parts of the intervertebral discs. Although commonly thought of as being made up of hyaline cartilage analogous to that of articular surfaces of joints, in fact, they are quite distinct. Cartilaginous end-plates are not freely articulating, but are blended with coarse collagen strands connecting the cartilage surface with the nucleus pulposus.
In addition, the end-plates give rise to chondrocyte-like cells found throughout nucleus pulposus. The cells are capable of producing and maintaining extracellular matrix as evidenced by the presence of Golgi cisternae and well-developed endoplasmic reticulum. Since some of these cells are necrotic, it follows that these are replaced by new cells originating from the cartilaginous end-plate. Utilization of the biologic properties of this tissue giving rise to these cells constitutes the basis for the present invention.